1. Field of the Invention
This invention relates to a lubricating composition having improved low and high temperature properties, to its method of preparation, and to its use, particularly as an open gear lubricant.
2. Description of Related Art
Frequently, lubricating compositions are used in applications that require satisfactory performance at both hot and cold temperature extremes. Examples of these applications include swing gears on mine shovels, large open gears on ball mills, and the like. A major complaint by users of this type of product is that it becomes very brittle at cold temperatures and tends to "run-off" at warmer temperatures.
Various combinations of additives have been suggested to rectify this problem. For example, U.S. Pat. No. 3,705,853 discloses a grease composition comprising a lubricating oil, a thickener, and an ethylene terpolymer having a Melt Index in the range of 0.5 to 200. Although viscosity index agents may be present, there is no mention of the grease containing an ethylene copolymer (See also U.S. Pat. No. 3,904,534).
However, ethylene copolymers have been incorporated into a variety of lubricating compositions. For example, U.S. Pat. No. 4,115,343 discloses that the storage stability and antifoaming tendency of organosiloxane polymers in mineral oil can be improved by adding ethylene-vinyl acetate copolymer (EVA) to the dispersion. As another example, U.S. Pat. No. 3,250,714 discloses that EVA is a VI improver for mineral lubricating oils. However, no mention is made of the Melt Index of the polymer. In U.S. Pat. No. 3,947,368, EVA having a Melt Index of from 5 to 580 is used as a pour point depressant in waxy lube oils. No mention is made, however, of a thickener being present.
Therefore, none of these references teach or suggest a lubricating composition having the excellent low temperature slumpability and high temperature adhesiveness of the composition described hereinafter.